Specifically, though not exclusively, the invention is particularly applicable in the field of loading devices structured for arranging internally of the forming cells of the die, and generally above a previously-laid layer (constituted by larger-grain support material), a further layer of powder material, generally finer and of better quality, which is destined to form the decorated surface of the tile which will be in view.
Devices of this type are known, generally referred-to as double-loading devices, and combine with a usual press-loading tray or truck various devices, among which small conveyor belts which, working in synchrony with the tray or truck, carry out the above-mentioned double-loading operation by depositing a further layer of powder in the cell, previously-filled from the tray.
The main limitation in the prior art consists in the considerable deformation which the decoration (in powder-form) is subject to when it is dropped from the end of the conveyor belt during the latter""s horizontal passing movement over the forming cell.
In effect this passing movement creates a sort of xe2x80x9cwaterfallxe2x80x9d effect, causing an undesired remixing of the powders which is further accentuated by the impact of the falling powders (the second load) on the underlying powders already deposited on the bottom of the cell from the first loading operation. The desired kinematic solution should be that the displacement speed (retreat) of the conveyor belt is equal and opposite to the transport speed of the belt on which the powders are deposited. This condition, however, is increasingly more difficult to maintain as the speeds increase.
A further drawback in the prior art is that the unloading times are quite considerable and add to work-cycle times.
The main aim of the present invention is to obviate the above drawbacks in the prior art by providing a process for depositing the powders which does not alter in any significant way the structure of the layer that is deposited.
An advantage of the invention consists in its being applicable to any existing type of ceramic press.
A further advantage of the invention is that it enables a true and proper decoration line to be set up, directly applied on the upper branch of the conveyor belt and composed of a plurality of decorator devices which can therefore produce different decorations. The number of possible decorations, however, does not in any way influence the work cycle time.
These aims and advantages and more besides are all attained by the present invention, as it is characterised in the appended claims.
The invention relates to a process for loading dies for forming ceramic tiles, of a type where a layer of powders bearing a decoration is laid on a rest surface of a conveyor belt, the conveyor belt is introduced between a bottom die and a top die above a cell afforded in the bottom die, and the layer of powders is dropped into the cell as the conveyor belt is retreated; characterised in that at least a retraction of the unloading end of the belt conveyor occurs without any relative dragging between the rest surface and a bottom of the layer by means of a translation of the unloading end, which is parallel to the rest surface and which retraction is characterised by being very rapidly executed.